package cn.ms.gateway.common;

/**
 * 分布式高效有序ID生产黑科技(sequence)
 * 
 * @author lry
 */
public class TradeIdWorker {

	private final long twepoch = 1288834974657L;
	private final long workerIdBits = 5L;
	private final long datacenterIdBits = 5L;
	private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
	private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
	private final long sequenceBits = 12L;
	private final long workerIdShift = sequenceBits;
	private final long datacenterIdShift = sequenceBits + workerIdBits;
	private final long timestampLeftShift = sequenceBits + workerIdBits
			+ datacenterIdBits;
	private final long sequenceMask = -1L ^ (-1L << sequenceBits);

	private long workerId;
	private long datacenterId;
	private long sequence = 0L;
	private long lastTimestamp = -1L;

	/**
	 * @param workerId
	 *            工作机器ID
	 * @param datacenterId
	 *            序列号
	 */
	public TradeIdWorker(long workerId, long datacenterId) {
		if (workerId > maxWorkerId || workerId < 0) {
			throw new IllegalArgumentException(String.format(
					"worker Id can't be greater than %d or less than 0",
					maxWorkerId));
		}
		if (datacenterId > maxDatacenterId || datacenterId < 0) {
			throw new IllegalArgumentException(String.format(
					"datacenter Id can't be greater than %d or less than 0",
					maxDatacenterId));
		}
		this.workerId = workerId;
		this.datacenterId = datacenterId;
	}

	/**
	 * 获取下一个ID
	 * 
	 * @return
	 */
	public synchronized long nextId() {
		long timestamp = timeGen();
		if (timestamp < lastTimestamp) {
			throw new RuntimeException(
					String.format(
							"Clock moved backwards. Refusing to generate id for %d milliseconds",
							lastTimestamp - timestamp));
		}
		if (lastTimestamp == timestamp) {
			sequence = (sequence + 1) & sequenceMask;
			if (sequence == 0) {
				timestamp = tilNextMillis(lastTimestamp);
			}
		} else {
			sequence = 0L;
		}

		lastTimestamp = timestamp;

		return ((timestamp - twepoch) << timestampLeftShift)
				| (datacenterId << datacenterIdShift)
				| (workerId << workerIdShift) | sequence;
	}

	protected long tilNextMillis(long lastTimestamp) {
		long timestamp = timeGen();
		while (timestamp <= lastTimestamp) {
			timestamp = timeGen();
		}
		return timestamp;
	}

	protected long timeGen() {
		return System.currentTimeMillis();
	}

}
